The present invention relates to an insertion box used in dissemination of radio frequency (RF) signals, such as might be performed by a cable television routing station. The present invention relates more particularly to an insertion box utilizing RF splitting and combining circuitry exhibiting low loss levels.
A cable television routing station receives a plurality of television signals, and directs an appropriate subset of those signals to cable television networking equipment in various communities. Ultimately, the signals are transmitted from the networking equipment in the various communities to subscribers. The task of disseminating the RF signals (television signals) to appropriate communities is typically accomplished by feeding each of the available RF signals to discrete combining and splitting modules, which are strung together to achieve a desired set of resulting outputs, each of which has an appropriate subset of television signals.
FIG. 1 illustrates the functionality of a simple cable television routing station. The routing station 100 receives three signals (channels 4, 5, and 6) and serves two communities (communities A and B). An actual cable television routing station would receive many more signals and serve many more communities. Per this simplified example, community A is to receive channels 4 and 6, while community B is to receive channels 4 and 5. To accomplish this dissemination task, the routing station 100 may employ a splitting module 102 and two combining modules 104 and 106. Splitting module 102 receives channel 4 and splits the RF signal, delivering channel 4 to each of combiners 104 and 106. In addition to receiving channel 4 as an input, combiner 104 also receives channel 6. Combiner 104 combines the signals received at its input, yielding channels 4 and 6 at its output. The output of combiner 104 is directed to network equipment that serves community A. Similarly, combiner 106 receives channels 4 and 5 as inputs, and combines those signals. The output of combiner 106 is directed to network equipment that serves community B.
Ordinarily, the combiners and splitters (such as splitter 102 and combiners 104 and 106) at a routing station are embodied as individual modules, which are housed in racks. Coaxial cables are used to route signals to and from the individual modules. Thus, desired splitting and combining functionality is accomplished via interconnecting individual splitting and combining modules with RF cables.
The foregoing practice exhibits certain shortcomings. A great number of individual splitting and combining modules are necessary to provide desired dissemination functionality for a routing station. Accordingly, these modules consume a considerable amount of space. Further, each time a signal is directed through a splitter or combiner module, a certain loss is incurred.
As the foregoing makes evident, there exists a need for a scheme by which RF signals may be disseminated while making use of a minimal number of individual splitting and combining modules, and while introducing a minimal amount of signal loss.
Against this backdrop, the present invention was developed. An insertion box solving the aforementioned problems may include a plurality of output ports. Each output port may be coupled to an output line that exhibits a characteristic impedance. The insertion box may also include a plurality of input ports. Each input port may also be coupled to an input line that exhibits the aforementioned characteristic impedance. Each input port corresponds with a predefined and unchanging set of output ports, so that a radio frequency (RF) signal conducted to a particular input port is conducted from the corresponding set of output ports. An RF circuit is interposed between the input ports and the output ports. The RF circuit effects the correspondence between input ports and output ports. The RF circuit includes splitter circuits and combiner circuits. At least one splitter circuit exhibits an input impedance less than the aforementioned characteristic impedance. Also, at least one combiner circuit exhibits an output impedance less than the aforementioned characteristic impedance.
According to another embodiment of the present invention, an RF circuit may include a combiner-splitter pair, which may itself include a first transformer having a first winding and a second winding. Each winding may have an input end and an output end. The output ends of the first and second windings are joined, creating a combiner output. The combiner-splitter pair may also include a second transformer having a third winding and a fourth winding. Each winding may have an input end and an output end. The input ends of the third and fourth windings are joined, creating a splitter input. The splitter input is attached to the combiner output.
According to yet another embodiment of the present invention, a method of disseminating a plurality of RF signals from a plurality of input lines to a plurality of output lines may include receiving, from one of the plurality of input lines, a first signal. The first signal may be split along first and second conduction paths. The signal propagating along the first conduction path may be received and combined with a second signal, yielding an output signal delivered from a combiner exhibiting an output impedance that is one-half of its input impedance. The output signal may be split, yielding a split output signal delivered from a splitter exhibiting an output impedance that is twice its input impedance. The split output signal may be disseminated to a plurality of output lines.
According to yet another embodiment of the present invention, an insertion box may include a plurality of output ports. Each output port may be coupled to an output line that exhibits a characteristic impedance. The insertion box may also include a plurality of input ports. Each input port may be coupled to an input line that exhibits the aforementioned characteristic impedance. Each input port corresponds with a set of output ports, so that a radio frequency (RF) signal conducted to a particular input port is conducted from the corresponding set of output ports. An RF circuit is interposed between the input ports and the output ports. The RF circuit effects said correspondence between input ports and output ports. The RF circuit comprises a means for combining and splitting RF signals without using a magnetic core to convert an output impedance of the means for combining to match an input impedance of the means for splitting.